There are known knowns: Donald Rumsfeld, 78, is a two-time former defense secretary who just penned his memoir, “Known and Unknown” ($36, Sentinel). There are known unknowns: most involve Iraq, but big-name journalists already asked those questions. So, Express asked Rumsfeld the double unknowns and found that the Pentagon’s former tough guy has a soft spot for Maria von Trapp.

You must be exhausted by all these interviews. Have you missed the media these past four years? [Laughter.] It’s been quite an experience. I’ve never written a book before. But we’ve been making the rounds. I really enjoyed Jon Stewart’s show last night. He’s very smart and quick.

In your book, you share “Rumsfeld’s rules,” or the witty one-liners you live by. Do you have a favorite rule for life? I think the most important rule is the Golden Rule. But another one is “What you measure improves.” In the military, they say it slightly different. They say, “You get what you inspect, rather than what you expect.” Why is that important? Well, if you’re going to measure something, you have to decide what it is you’re going to measure. You have to have priorities. You have to make choices, and making choices is hard because you can make the wrong choices. But once you make a choice and track your progress against a choice, it does get better.

Naming your Memoir “Known and Unknown,” you must have a great sense of humor. Well, in the author’s note, I trace the history of that phrase. The first time a group of us started talking that way was when I was chairing the Ballistic Missile Commission in the ’90s. We were dealing with intelligence analysts, and it became very clear that there were things we knew we knew, things we knew we didn’t know and things we didn’t know we didn’t know, and it’s that last category that can cause the real problems.

In your career, did you ever have a moment when you pinched yourself and thought, “I can’t believe this is my life?” You write about being friends with Sammy Davis Jr. and meeting everyone from Elvis to Saddam Hussein. Is there a moment that sticks out in your memory? The most amazing moment for me was when I was first elected to Congress at the age of 30. I was described by someone writing their doctoral dissertation as, “Being distinguished principally by my total lack of social, financial, and political standing in the community.” I woke [my wife] Joyce up and said, “Listen to this!” And she said, “Don, go back to sleep. It’s tough to argue with!” [Laughter.] But being elected, to be that human link between hundreds of thousands of people and their federal government was really a high privilege.

And you ran for president briefly in 1988. Do you regret that you were never president? No, no. In my life, I just feel so fortunate to have been able to do the things I’ve done. Some things didn’t work out, but you just pick yourself up and go on from there.

You’ve met so many world leaders past and present. Who’s the oddest world leader you’ve met? Well, now, isn’t that an interesting question? I guess I don’t think of people as odd. They all came from different cultures and different histories and backgrounds. What’s odd? I’m sure they look at us and think we’re odd.

Who was the most impressive? Certainly, one of the more impressive was Anwar Sadat, the president of Egypt who made a peace agreement with Israel. And the sultan of Oman, Sultan Qaboos, was very thoughtful after September 11th.

You knew many of them, but who’s the most underrated historical figure of the 20th century? My goodness, well, in this past century, Ronald Reagan was described and criticized by the press, called an “amiable dunce.” But he wasn’t. He was a strategic thinker. His letters show him to be a man of considerable thoughtfulness, and he was underrated in the country. Gerald Ford was certainly underrated. What he did to restore the reservoir of trust in America after succeeding the only man in our history to resign was very impressive.

You’ve worked in and studied the region for four decades. What’s your view on the current turmoil in the Middle East? I think anyone who thinks they know is probably going to be wrong. I don’t know how it’s going to turn out. I think what you’re seeing is that you’ve got a very large collection of people who are unemployed. They’re living in countries that don’t have the kinds of opportunities that we have in freer countries like ours. When they don’t have the opportunities that we do, they either try to leave and come to our country or Western Europe, or it boils over at some point.

A lot of the leaders in the region have not moved at a fast-enough pace towards free economic and political systems, and they’re paying the penalty. Some of them had close relationships with us. Some of them contributed to greater stability in the region, certainly the peace agreement that Anwar Sadat entered into with Israel contributed to a more stable region. But you’re now seeing the people throwing their leaders out and looking for something different. The risk, of course, is you’ll end up like Lebanon, where they had the Cedar Revolution and ended up with Hezbollah, a terrorist organization, an oppressive organization, running Lebanon. Same thing in Iran. The people were striving for something different, and now you have a handful of dictatorial ayatollahs running the country. One has to hope that that won’t be the result in countries like Egypt.

On a more personal note, you’ve been married for almost 60 years. Your political life must have been hard on your wife, Joyce. How did you stay married so long? I would say it was our great good fortune. She, when asked, would say, “He travels a lot.” She’d say it with a smile, of course.

Have you seen any good movies lately? I see very, very few movies, but I watched “Secretariat” not too long ago and enjoyed it. I may go to a theater once a year. The other movie I saw recently was “True Grit,” but that was the old “True Grit,” not the new one.

Do you have a favorite film? I really don’t. This sounds silly, but I must say, I did like “The Sound of Music!” [Laughter] But I haven’t seen it in decades.

You’ve lived and traveled all over the world. Do you have a favorite vacation spot? Our home is our favorite spot, and that’s now Taos, New Mexico. We love the mountains and the culture and the skiing, and feel very fortunate to be able to be there.

You cite Whittaker Chambers’ “Witness” as an important book. Do you have any other books you recommend? Well, I like biographies. Biographies, as some wise man once said, are really history without theory, I enjoyed Ulysses S. Grant’s memoirs. I liked Jean Edward Smith’s books on Grant and FDR. I’m reading a book on D-Day right now. A couple weeks ago I read the book “Citizens of London” about Edward R. Murrow and Ambassador Winant and Averell Harriman. I don’t read much fiction. I love history.

And how important is studying history? I hope that the youngsters in America do study history and do read biographies. I think it’s important that they be rooted in what’s going on in the world and understand it clearly. That’s one of the reasons I spent the last four years writing my memoir, and putting up a website with hundreds of documents on it and thousands of pages, so people can go in and see what it’s like to be on the inside. To see what it’s like to watch policymakers and presidents make tough decisions, knowing that they have imperfect information.

Now that you’ve written a book, do you wish you had tried sooner? No, it took me full time with some wonderful people helping me and fact-checking and digitizing my archive. I just hope people will go into the website, Rumsfeld.com, and see the actual documents that were going back and forth in government during these important periods in our history.

Are you enjoying retirement or going stir-crazy? Oh, no, I’d never go stir-crazy! Joyce and I have our foundation that supports charities for the troops, where the proceeds of my book are going. We also have a Central Asian fellowship program. We’re supporting young people seeking out Ph.D.s and higher education, and we’re supporting microfinance in 12 to 15 countries around the world. We’re doing a lot of interesting things; we’ve been very fortunate in life.

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